Influenza has a long history of pandemics, epidemics, resurgences and outbreaks. Avian influenza, including the H5N1 strain, is a highly contagious and potentially fatal pathogen, but it currently has only a limited ability to infect humans. However, avian flu viruses have historically observed to accumulate mutations that alter its host specificity and allow it to readily infect humans. In fact, two of the major flu pandemics of the last century originated from avian flu viruses that changed their genetic makeup to allow for human infection.
There is a significant concern that the current H5N1, H7N7, H9N2 and H2N2 avian influenza strains might accumulate mutations that alter their host specificity and allow them to readily infect humans. Therefore, there is a need to assess whether the HA protein in these strains can, in fact, convert to a form that can readily infect humans, and a further need to identify HA variants with such ability. There is a further need to understand the characteristics of HA proteins generally that allow or prohibit infection of different subjects, particularly humans. There is also a need for vaccines and therapeutic strategies for effective treatment or delay of onset of disease caused by influenza virus.